Dry mold under floorboards too expensive to remove safe?

Hello, we had some rain water flood our balcony and then our living room wood floor for several seconds before pushing the water out and inevitably some water fell under the floorboards through the gaps. Next summer the floor became wobbly and when I made a small hole to ventilate the floor and put my phone camera in to look underneath I realized that the timber joists that hold up the wood floor have all turned dark grey or black. Following that, we made several ventilation holes at the edges of the floor and since have maintained humidity under 55% for the past 2 years and there has been no smell or indication of active mold whatsoeverbut the joists under the floorboards still remain black and I'm wondering if the completely dried out and inactive mold can still cause health problems. I myself feel I have nasal inflammation rather constantly... The house is a rental and the owner is not willing to replace the timber floors since the flooding was our fault